SEISMIC STRATIGRAPHY AND PALAEOENVIRONMENTS OF QUATERNARY INCISED-VALLEY SYSTEMS IN THE EASTERN ENGLISH CHANNEL

This paper presents the results of research into the nature and origin of the Quaternary incised-valleys in the Eastern English Channel (EEC).

During the Quaternary the area of the EEC on the European continental shelf has fluctuated between marine and terrestrial conditions due to glacial-eustatic variations. These variations mean that in the EEC during the cold glacial maxima, sub aerial inner continental shelf conditions prevailed and large rivers eroded out fluvial valley systems. These systems were subsequently infilled by sediments from cold stage terrestrial and fluvial systems, and marine deposits accumulating during intervening transgressive interglacial phases. The aims of this research are to examine the nature and extent of these palaeovalley systems in the EEC. This will hopefully lead to a to better understanding of their age and origins.

Some 1000 km line of high-resolution shallow seismic profile have been used to establish the geometry and bedrock bounding surface of these Quaternary formations. Sediment isopachyte, and depth to rockhead mapping reveals the extent and depth of incised-valley features below the seabed. The data has revealed palaeovalleys up to 5 km wide, infilled with 30 m of sediment in places. Interpretation of shallow seismic and lithostratigraphic data, retrieved from sequences in water depths ranging from –30 m to –50 m, indicates formation during multiple cut-and-fill events. The complex facies architecture includes coarse gravels, fine sands and silts, as well as organic peat deposits, indicating a broad range of depositional environments. Biostratigraphical analyses of vibrocore samples provide palaeoenvironmental reconstructions of the infill sequences. Aminostratigraphy will hopefully provide age control.